The Turkish Delight that Edmund sells out his siblings for in The Lion, the Witch, and the Wardrobe is quite possibly one of the most famous specific food-related moments in fantasy and science fiction. Growing up, I thought it seemed like the world's most wonderful food, and just like Edmund, I would have done a lot just to get a taste.
Then, when I was in grad school, I had the chance to try some at an end-of-semester party in one of my classes. It was a huge disappointment. I think I had been imagining something like baklava (which, incidentally, I would betray almost anyone for), and it ended up being this weird, tasteless, candied jelly that was covered in dry powdered sugar. Not awesome. Maybe I just got a bad batch, but my dreams of a fantastic food worth turning evil to get were totally shattered.
Fortunately for me, fantasy and science fiction fans seem to be a culinarily creative bunch, and with a bit of looking, I've found quite a few food-related products with a fantasy/scifi theme...